The dramatic melting of Arctic ice is already driving extreme weather that affects hundreds of millions of people across North America, Europe and Asia, leading climate scientists have told the Guardian.

Severe “snowmageddon” winters are now strongly linked to soaring polar temperatures, say researchers, with deadly summer heatwaves and torrential floods also probably linked. The scientists now fear the Arctic meltdown has kickstarted abrupt changes in the planet’s swirling atmosphere, bringing extreme weather in heavily populated areas to the boil.

The northern ice cap has been shrinking since the 1970s, with global warming driving the loss of about three-quarters of its volume so far. But the recent heat in the Arctic has shocked scientists, with temperatures 33C above average in parts of the Russian Arctic and 20C higher in some other places.

In November, ice levels hit a record low, and we are now in “uncharted territory”, said Prof Jennifer Francis, an Arctic climate expert at Rutgers University in the US, who first became interested in the region when she sailed through it on a round-the-world trip in the 1980s.